The present invention relates to a hydraulic controller which comprises a choking element for an internal oil passage (especially, a choking element that is generally referred to as xe2x80x9cchoke passagexe2x80x9d).
Furthermore, the present invention relates to a hydraulic controller which generates a signal pressure by using an above mentioned choking element so as to control the operation of a transmission. The present invention relates particularly to a hydraulic controller which provides a signal pressure that corresponds to the rotation of the engine and is used, for example, for operating the starting clutch of the transmission.
For hydraulically executing the shift control of a transmission, various types of hydraulic controller have been known, and hydraulic controllers have been incorporated in transmissions for hydraulic shift control. Such a hydraulic controller includes a regulator valve, which is used to adjust and produce a line pressure from oil supplied by an oil pump. This line pressure is then used for producing various control pressures to execute, for example, the shift control of the transmission. The part of the oil that is supplied from the pump to the regulator valve but not used for the line pressure to execute various control operations is discharged from the regulator valve. This discharged oil is used for lubricating the internal mechanisms of the transmission. For performing the lubrication, the hydraulic controller includes various lubrication control valves to control appropriately the pressure necessary for distributing a predetermined amount of lubrication oil to each internal mechanism.
In many cases, such a hydraulic controller includes many choking elements (various orifices and chokes), which are provided to oil passages in the transmission. For example, Japanese Laid-Open Patent Publication No. H04(1992)-254057 discloses a hydraulic controller which has hydraulic control valves and a separator plate between them on a side of the housing of the transmission. In this hydraulic controller, the separator plate is provided with a plurality of small apertures, i.e., choking elements (orifices).
Choking elements can be provided in this way, i.e., as orifices formed in the separator plate, but the choking elements provided in this way cannot be highly viscosity-sensitive choking elements, i.e., choking elements whose passage lengths are longer than their diameters, disclosed, for example, in Japanese Utility-Model Publication No. H07(1995)-20437. By the way, a control valve can be provided with a choking element formed in the valve body thereof. However, choking elements are small apertures, so it is difficult to form choking elements in a casting process. They must be formed by machining, for example, by drilling. As choking elements are difficult to form, the machining cost is relatively high.
Furthermore, if apertures formed in the separator plate are to be used as orifices, then the apertures must be connected to oil passages provided on one side of the separator plate and to other oil passages provided on the other side thereof, so that oil can flow continuously. Because of this reason, if orifices are to be provided in passages formed in the valve body that is provided on one side of the separator plate, then it is relatively difficult to use small apertures formed in the separator plate as orifices.
Moreover, generally, a vehicular transmission comprises a starting clutch, which is provided between the input member and the output member of the transmission, the input member being driven by a prime mover (engine) and the output member being connected to wheels of a vehicle. In this arrangement, the starting clutch typically being actuated hydraulically controls the engagement of the input and output members, for example, in starting or stopping the vehicle. Such an engagement control is executed generally in correspondence to the rotational speed of the prime mover. In such a case, the rotational speed of the prime mover is detected by a sensor, which generates a signal representing the rotational speed. This signal is used to control the operation of an electrically controlled valve, which produces a control pressure used for the engagement control.
In such a hydraulic control that utilizes an electrically controlled valve, a control failure can occur if electrical trouble (for example, a problem that the control system cannot start up) or an open stick (a condition where a valve spool sticks and stays open) happens. To avoid a control failure, the controller is often equipped with a backup system that utilizes a valve to generate a signal pressure in correspondence to the rotational speed of the prime mover, and then this signal pressure is used for the engagement control in backup operations. For example, a Pitot-tube is used to generate the signal pressure for the execution of the engagement control (refer to Japanese Laid-Open Utility-Model Publication No. S63(1988)-30662, Japanese Laid-Open Patent Publication No. H06(1994)-26565, etc.). However, this arrangement presents a new problem of the size of the transmission becoming large as it requires a space for the placement of a Pitot-flange.
In consideration of the above disadvantages, the applicant of the present invention has proposed a hydraulic controller disclosed in Japanese Laid-Open Patent Publication No. H11(1999)-257445. This hydraulic controller comprises an oil pump which is driven by the engine to deliver oil by the amount that corresponds to the rotational speed of the engine. The oil delivered from the oil pump is led into an oil passage with an orifice, and the above mentioned signal pressure for the engagement control is produced from the pressure difference created by the orifice, i.e., the difference in the pressure before and after the orifice in the flow.
As long as the temperature and viscosity of the oil does not change, the pressure difference created by the orifice changes in correspondence to the flow of the oil. This condition enables the production of the signal pressure that corresponds to the flow of the oil, i.e., to the rotational speed of the engine, which drives the oil pump. However, if the temperature of the oil changes, and the viscosity changes accordingly, then there is a change in the pressure difference even though the flow is kept constant. Because of this adverse effect, the signal pressure produced through the orifice when the oil is at a low temperature is higher than when the oil is at a high temperature. If the signal pressure is used in this condition, then the engagement control is not performed smoothly.
It is an object of the present invention to provide a hydraulic controller which utilizes a choking element formed in a separator plate.
It is another object of the present invention to provide a hydraulic controller whose construction enables formation of a choking element in a separator plate, for a passage provided in a valve body, which is provided on one side of the separator plate.
It is yet another object of the present invention to provide a hydraulic controller which always produces a signal pressure that corresponds to the rotation of the engine, from a pressure difference created through an orifice even though the temperature of the oil fluctuates.
A hydraulic controller according to the present invention is equipped with a first valve body, a second valve body and a separator plate, which is sandwiched between the first and second valve bodies. Also, the hydraulic controller comprises an upstream hydraulic control element (for example, the SC shift valve 92 described in the following preferred embodiment), a downstream hydraulic control element (for example, the SC backup valve 94 in the following embodiment), a connection oil passage (for example, oil passage 103 in the following embodiment) and a choking element (for example, the choke 75 in the following embodiment). The upstream hydraulic control element is provided on an upstream side for hydraulic control either in the first or second valve body, and the downstream hydraulic control element is provided on an downstream side for hydraulic control either in the first or second valve body. The connection oil passage connects the upstream hydraulic control element and the downstream hydraulic control element, and the choking element is placed in the connection oil passage. For this arrangement, the separator plate is provided with a slot-like opening (for example, the choke opening 75a in the following embodiment). In the assembled condition, where the separator plate is sandwiched between the first and second valve bodies, the part of the connection oil passage connecting to the upstream hydraulic control element is in fluid communication with one end of the slot-like opening while the part of the connection oil passage connecting to the downstream hydraulic control element is in fluid communication with the other end of the slot-like opening. As a result, a long narrow room created by the slot-like opening of the separator plate between the first and second valve bodies comprises the choking element.
In this hydraulic controller, oil flowing through the connection oil passage from the upstream hydraulic control element enters the slot-like opening at one end thereof and flows to the other end thereof and then flows through the connection oil passage connected thereto to the downstream hydraulic control element. In this case, the slot-like opening is a long narrow room created between the first and second valve bodies, so it provides a long choking route. In other words, the hydraulic controller according to the present invention comprises a choking element that is provided as a slot-like opening formed in the separator plate.
In this hydraulic controller, if the upstream and downstream hydraulic control elements are provided in the first valve body, and also the connection oil passage is formed in the first valve body, then preferably, the part of the connection oil passage connecting to the upstream hydraulic control element be formed in the first valve body, opening at a position which will meet one end of the slot-like opening. Preferably, the part of the connection oil passage connecting to the downstream hydraulic control element be also formed in the first valve body, opening at a position which will meet the other end of the slot-like opening.
With this arrangement, even if the first and second valve bodies and the connection oil passage are provided only in the first valve body, which is placed on one side of the separator plate, the slot-like opening formed in the separator plate can be still used as a choke which is provided in the connection oil passage.
According to another feature of the present invention, the hydraulic controller comprises a regulator valve, a group of control valves including at least a electrically controlled valve, and a discharge passage (for example, oil passage 102 in the following embodiment). The regulator valve generates a line pressure PL by adjusting the pressure of the oil delivered from an oil pump, which is driven by a prime mover. The group of control valves control the operation of a transmission by receiving the line pressure, and the discharge passage leads excess oil whose pressure is adjusted from the line pressure by the regulator valve. Furthermore, the discharge passage is bifurcated into a first branched discharge passage (for example, oil passage 102a and oil passage 105 in the following embodiment) and into a second branched discharge passage (for example, oil passage 103 in the following embodiment). The first branched discharge passage is provided with an on-off valve (for example, the SC shift valve 92 in the following embodiment), which closes the first branched discharge passage upon receiving a pressure generated in an event of failure of the electrically controlled valve. The second branched discharge passage is provided with a first orifice (for example, the first orifice 66 in the following embodiment). In addition, the hydraulic controller further comprises a signal pressure generating valve (for example, the SC backup valve 94 in the following embodiment), which generates a signal pressure in correspondence with the pressure difference existing through the first orifice of the second branched discharge passage. Furthermore, the second branched discharge passage is provided with a choke (for example, the choke 75 in the following embodiment), which is provided upstream to the first orifice.
In this arrangement, at least part of the above mentioned regulator valve, group of control valves and discharge passage is formed in a structure composed of the separator plate and the first and second valve bodies, which sandwich the separator plate, such that the above mentioned choke comprises the choking element (i.e., a long narrow room formed by the slot-like opening between the first and second valve bodies).
The hydraulic controller with this arrangement performs the engagement control of the starting clutch, etc. with a signal pressure generated in correspondence to the rotation of the engine by the electrically controlled valve in normal condition (i.e., while the electrically controlled valve operates normally with no electrical failure). In this condition, the on-off valve keeps the first branched discharge passage open, so the excess oil from the regulator valve is led through the first branched discharge passage and supplied as lubrication oil. Oil can be discharged though the second branched discharge passage, but the first orifice provided in the second branched discharge passage is a relatively large resistance to the flow. Therefore, oil is discharged mainly through the first branched discharge passage.
However, if there is an electrical failure, the electrically controlled valve cannot generate the signal pressure that corresponds to the rotation of the engine. In this case, the on-off valve closes the first branched discharge passage to lead the excess oil from the regulator valve to the second branched discharge passage. As a result, a pressure difference is created through the first orifice of the second branched discharge passage correspondingly to the flow, and then a signal pressure which corresponds to this pressure difference is generated by the signal pressure generating valve. Because this flow, i.e., the flow of the excess oil from the regulator valve, corresponds to the discharge of the oil pump, which is driven by the engine, this signal pressure is used, for example, for the engagement control of the starting clutch, as rotation-responding pressure that corresponds to the rotation of the engine.
In addition, to avoid a problem of fluctuations in the pressure difference through the first orifice caused by oil temperature changes which change the viscosity of the oil, the hydraulic controller according to the present invention has a choke, which is provided upstream to the first orifice on the second branched discharge passage. This choke functions to change the flow of oil through the first orifice when the temperature of the oil changes. In this way, the effect of the temperature change on the hydraulic controller is minimized to acquire the signal pressure that always corresponds to the rotation of the engine.
It is preferable that the second branched discharge passage be provided with a bypass passage (for example, oil passage 104a in the following embodiment) which connects a point upstream to the choke and a point downstream to the first orifice and that this bypass passage be provided with a second orifice (for example, the second orifice 67 in the following embodiment). Furthermore, preferably, the hydraulic controller be arranged to function in such a way that after the on-off valve has closed the first branched discharge passage by receiving a pressure generated because of a failure of the electrically controlled valve, when the pressure upstream to the choke of the second branched discharge passage increases to a predetermined pressure, the on-off valve is opened by this increased pressure upstream to the choke. With this arrangement, when the viscosity of the oil changes because of a change in the oil temperature, and because of this viscosity change, the pressure upstream to the choke changes. As a result, the flow through the bypass passage is changed. Also, by opening the on-off valve, the oil can be led to the first branched discharge passage. As a result, the effect of the oil temperature change on the pressure difference existing through the first orifice can be further minimized to keep the signal pressure generated from the signal pressure generating valve immune to the oil temperature fluctuation, so the signal pressure always corresponds to the rotational speed of the engine.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.